Air sweetening



United States Patent O 3,092,569 AER SWEETENENG Charles (l. Petty, La Gloria Gm @l @il Co., f9.0. Rox 840, Tyler, Tex. Filed Dec. 18, 1959, Ser. No, 860,601 6 (liaims. {Ci. 20S-2:04)

This invention relates to catalytic air sweetening of sour liquid hydrocarbon and particularly to the use of aryl mercaptan in aqueous caustic as catalyst for the air sweetening. It further relates to the use of -aryl mercaptan as catalyst for air sweetening las :a preliminary treatment `followed by additional sweetening with other sweetening agents for improved sweetening of naphthas.

This mercaptan air sweetening step can generally be applied as a complete sweetening treatment of easily sweetened sour naphthas or as a preliminary treatment for more diiiicultly sweetened naphthas, allowing reduction in the usually necessary quantity of known sweetening agents in this combined use, an increase in the rate of air sweetening, better mercaptan oxidation and consequent all-over improvement in sweetening economy for sour naphthas of various types.

A most common approach to sweetening has been oxidation of -mercaptan contained in the sour naphtha and efforts to effect that oxidation with greatest economy has dictated the use of air. Equivalent oxidizing agents such as oxygen or air-contained ozone and sometimes oxides of nitrogen `can be used, but these acidic oxides of nitrogen may react with caustic and tend to reduce the economy.

That oxidation, performed upon naphthas often readily oxidizable, also tends to oxidize the hydrocarbon and increase its tendency towards formation of objectionable gum in storage, reduction of color and lowering of gasoline octane as well as lead susceptibility. To prevent the air oxidation of the hydrocarbon, it has often been proposed to apply such air oxidation in conjunction with oxidation inhibitors. These may be aromatic amines, aromatic diamines, mono hydroxy phenols, polyhyd-roxy phenols, naphthols, amino phenols and their alkyl substituted derivatives. Nevertheless, the process has been expensive with respect to the extra quantity of inhibitor needed and uneconomic for the long treating time required for sweetening; for instance, naphtha air sweetened with diamines needed to be stored for long periods of time over caustic before adequate air sweetening was effected, even without considering the cost.

An important approach to improved sweetening economy is in the promoter catalytic eiect apparently exhibited by phenols, typically petroleum extracted acid oils, to directly accelerate the rate and extent of reaction of the sour mercaptan components in the naphtha, with epoxides such as alkylene oxides, as described and claimed in my prior Patent No. 2,862,804, issued December 2, 1958, whose disclosure is here incorporated by reference.

It is now found that considerably less sweetening agents of various types including epoxides, with or without a small content of phenols and alkyl phenols, are possible, using as preliminary air sweetening catalyst, an aromatic mercaptan.

According to this invention, it is `found that aryl mercaptans dissolved in strong aqueous caustic have an accelerating effect on the oxidation by air of any sour components, such as higher aliphatic mercaptans contained in caustic washed naphthas, particularly such as are preferentially soluble in naphtha and inextractaole with aqueous caustic.

The air oxidation according to this invention is rapidly catalyzed by the aryl mercaptan to quickly reduce the sour content for easily sweetened naphtha, such as light catalytic gasoline, so that such preliminary sweetening suffices to produce a commercially acceptable sweetened ice gasoline. Much improved sweetening for other sour liquid hydrocarbon normally difficult to sweeten is here also made available, even to produce a doctor-sweet product in a short time, using the aryl mercaptan catalyzed air sweetening as a preliminary step followed by subsequent steps of sweetening with known sweetening agents, whereby the combined treatment produces an improved sweetened product or a sweetened product more economically, even upon `diiiicultly sweetened hydrocarbon liquids, such as coker or thermally cracked naphthas.

Thus, according to this invention, certain easily sweetened hydrocarbon oils are treated with only a preliminary air oxidation, `scrubbing the air injected sour naphtha with strong aqueous caustic containing a controlled catalytic quantity of aryl mercaptan for a period of about 15 minutes to 2 hours at temperatures ranging from ambient to about 212 F. and at pressures suflicient to maintain the system liquid, usually from about 50-100 p.s.i. Thereby, a naphtha is most economically produced containing about 0.0002 to 0.0008 wt. percent RSH naphtha (as sulphur) which is useful for most commercial purposes without further sweetening. Suchtreatment is desirably used for light catalytic gasolines.

However, for more extensive sweetening for other sour liquid hydrocarbons, that aryl mercaptan catalyst air oxidized naphtha is given a further sweetening treatment such as adding another known sweetening agent and scrubhing with caustic. For instance, the partially sweetened hydrocarbon may have added epoxide, typically a lower alkylene oxide such as ethylene or propylene oxide, and then is scrubbed with aqueous caustic, preferably containing phenols as described in my prior patent; subsequent sweetening treatment may be with an arylene diamine, typically N,N' di-lower alkyl phenylene diamines in which the lower alkyl has about 1-9 carbon atoms such as N,N diisobutyl p-phenylene diamine, and mixtures of such typical epoxy and `arylene diamine sweetening agents for example, as disclosed in my prior copending applica- -tion 773,897 led November 14, 1958, now Patent 2,945,- 808, issued July 19, 1960, and here incorporated by reference. l

Polyhydric phenols such as pyrogallol, catechol, hydroquinone and their lower alkyl substituents such as tertiary butyl catechol, or 'amino phenols such as p-N-benzyl amino phenol and p-N butyl amino phenol are also useful sweetening agents for combined use with the aryl mercaptan catalyzed air sweetening and are best used in the aryl mercaptan aqueous caustic catalyst solution so that the catalyzed air sweetening and sweetening effect of such phenolics take place simultaneously. An advantage of this, it will be recognized, is that such phenolics have an inhibiting effect to produce a more stable fuel Yand one in which the air has not oxidized the hydrocarbon substance thereof.

Simple monohydric phenols and lower alkyl monohydric phenols such las may be derived by extraction from liquid petroleum hydrocarbon are also usefully used in various stages of the sweetening such as in the mercaptan caustic catalyst or such simple phenols usually in aqueous caustic are also used with or following subsequently applied sweetening agents where solution appears to promote catalytic sweetening effect. For instance, as taught in my prior application (above) and Patent 2,862,804, these phenols also catalyze the epoxide and diamine sweetening. ln some contrast, however, to the effect of other phenols dissolved in the causticmercaptan catalyst solution, these monohydric phenols become most active after substantial use ofthe catalyst, possibly after they have become oxidized per se. y

The aromatic mercaptan is applied to catalyze the sweetening in aqueous caustic solution ranging from 10-50 percent, preferably 25-40 wt. percent caustic such as the sodium hydroxide or potassium hydroxide in water. The aromatic mercaptan is maintained in the caustic, torl effective catalytic air sweetening purposes, in the range of from 0.1 to 10% by weight and usually in the range of 0.3 to 0.5% by weight of the caustic solution. Aromatic mercaptan is cheaply available from caustic which has been used in preliminary Washing to cheaply sweeten gasolines, using the spent caustic from this source. However, in use to catalyze the air sweetening, the caustic catalyst solution will soon become denuded of its elective aromatic mercaptan content by reaction with the sour components of the naphtha With which it is contacted, hence the aromatic mercaptan must be replenished from time to time to avoid loss of the catalytic electiveness of the caustic air sweetening catalyst solution.

As indicated, an important promoter eiiect on the `svveetening results when the catalyst solution contains simple phenols. Such monohydric phenols accelerate the rate and degree of oxidation of the air sweetening and appears to become more active as it ages in use, possibly by being oxidized itself. Such phenol may be present in any quantity from about 0.2 to 30 volume percent and preferably it is in the range of 2 to 20 volume percent of the aqueous caustic catalyst solution. Naphthas are a useful source of such phenols, and a preliminary caustic wash to remove sour components also suiiices to extract phenols whereby such spent caustic preliminary Wash solution is a preferred source; not only of aryl mercaptan, but also caustic extracted petroleum phenols. Such spent caustic added to the catalyst solution, when the aryl mercaptan content is to be increased, also imparts the phenol content of the spent caustic. Since the phenol content of the catalyst solution is not reduced in use, the phenol content of the catalyst solution may be initially low, about 0.2 percent, but becomes gradually increased with increments of spent caustic when that is used as the source of aryl mercaptan and/or phenol, That phenol is also useful in a caustic scrubber solutionI subsequently used in sweetening with organic epoxide or phenylene diamine. However, such caustic scrubber solution, in epoxide or diamine sweetening, desirably contains no aryl mercaptan. Hence, when spent caustic is the initial source, the aryl mercaptan is removed. A useful source of mercaptan free caustic-phenolate solution is the spent catalyst used in the air sweetening which has been denuded of its aryl mercaptan content in use. While these spent caustic solutions are desirable sources of aryl mercaptan and phenols for economy, this invention is not to be limited to this particular source of the reagents used. Y

The aryl mercaptans may be any, but preferably are' such as are extractable from naphtha with an aqueous caustic wash. This allows, most economically, a sour naphtha pretreatment with a simple caustic Wash to remove therefrom aqueous alkali soluble mercaptans including substantial quantities of aryl mercaptan, typically thiophenol, thiocresol, propylthiophenol and typically such lower alkyl thiophenols in which the meta isomers usually predominate. .Thereby the prewash is a useful source of aryl mercaptan catalyst, which may be used as the catalyst in the subsequent air oxidation of a naphtha for sweetening of its sour components. That preliminary caustic Wash used in the production of catalyst may also sulhce to produce a partially sweetened naphtha stock susceptible to further air oxidation sweetening catalyzed by the extracted aryl mercaptan. That preliminary caustic wash also produces a spent caustic which will contain phenols and alkyl phenols which further have a catalyzing elect upon the air oxidation.

In typical treatment, sour liquid hydrocarbon sucls naphtha is rst Washed With strong caustic, usuallyabout 30-40 wt. percent. Its temperature and pressure are adjusted. It is mixed with about 1A to 2 cu. ft. of air per barrel and passed to a catalyst scrubber in which it is scrubbed in the presence of the catalyst solution for the requisite time of 1,/4 to 2 hours, usually 30-60 minutes at moderate temperatures and pressures, preferably being up to 150 F. for gasolines and 90-212 F. for distillates and fuel oil at 50-100 p.s.i. Thereafter, the liquid hydrocarbon usually after removal of excess air can be treated with epoxide such as with an ethylene oxide solution in hydrocarbon, while being scrubbed With strong aqueous caustic containing 0.2-30 percent of phenols. The ethylene oxide solution is dissolved in the sour liquid hydrocarbon in quantity to impart 5 to 100 lbs. of ethylene oxide per 1000 barrels, usually 20 to 50 lbs. per. 1000 barrels, and the aqueous caustic scrubber solution contains to 50 percent, preferably 15 to 25% by Weight phenols, the air-treated gasoline is contacted with the catalyst solution containing additional quantities of polyhydric phenol such as catechol, hydroquinone, amino, phenol, etc., in quantity ranging from about 0.05 to 1.0 of Wt. percent, usually 0.1 to 0.5 wt. percent added directly to the pretreated naphtha or to the caustic scrubber solution.

The air sweetening eiect of the treatment with aryl mercaptan catalyzed caustic is illustrated in the following example and table attached.

EXAMPLE 1 A light catalytically cracked gasoline containing 0.0038 Wt. percent RSH as sulphur in volume percent is air mixed with 15 volume percent of an aqueous caustic catalyst solution by continuous air agitation eiected by bubbling air into the mixture. The catalytic mixture consists of 99.4 Volume percent of 36 B. caustic, 0.50 volume percent rnthiocresol and 0.10 volume percent of n-butyl mercaptan. Small samples of bothrthe gasoline and catalyst solutions were taken periodically and analyzed.r When the mercaptan content of the naphtha had been reduced to 0.0002 RSH Wt. percent as sulphur, an additional sample of the original gasoline was substituted, using the same catalyst solution, however, and the air agitation was continued. 'Ihe results and analyses are shown in the following Table 1.

Table l' Caustic Gasoline, Temp., Y Time F. Wt. Wt. Wt. Wt.

percent percent percent percent NaOH Aryl .alkyl Thiols Thiols Start. 30. 0 0. 38 0.07 0. 0038 5 min- 30.0 0. 36 0. 06 0.001 10 min 30. 0 0.30 0.06 0. 0006 15 min- 30. 0 0. 28 0. 05 0.0002 Start 100 30. 0 0. 28 0. 05 0. 0038 5 min 30.0 0.24 0.04 0.0011 10 min 30. 0 0. 18 0. 02 0. 0008 15 min 30. 0 0. 12 0. 02 0. 0003 Start- 100 30. 0 0. 12 0.02 0. 0038 5 min- 30. 0 0. 09 0.02 0.0012 l0 min- 30.0 0. 08 0. 02 0. 001 15 min- 30. 0 0.08 0. 02 0.0009 20 min- 30.0 0.06 0. 02 0. 0006 30 min 30.0 0. 05 0.01 0. 0004 45 mln- 30. 0 0. 04 0.01 0. 0002 Start- 100 30 0. 04 0. 01 0. 0038 15 min 30 0. 08 0.01 0. 0009 20 min l 30 0. 33 0. 01 0. 0001 1 Wt. percent M-thiocresol.

It ywill be noted that the time for reducing the initial RSH content of the gasoline withreach succeeding sample increased as the aryl mercaptan content of the catalyst became reduced. For instance, the third treatment required 45 minutes to reduce the mercaptan content of the naphtha t-o the same degree as required only minutes in the rst batch. In the fourth batch addition of more thiocresol reactivated the apparently inactive catalyst solution to its original activity. The presence of a small quantity of alkyl mercaptan in the catalyst solution did not have a comparative effect. This table clearly illustrated the catalytic eiect of aryl mercapt-an to accelerate air sweetening with caustic.

EXAMPLE 2 This is an example of commercial treatment of an easily sweetened commercial naphtha and reference is made to FIG. 1 of the ydrawings herewith, lwhich is a iiow diagram of this treatment upon a light catalytic cracked gasoline having a B.P. range of 90-370 F.; a preliminary catalytic air swcetening in the presence of aryl mercaptau is all the treatment that is given here for satisfactory commercial sweetening thereof. As shown in FIG. l, such light catalytic gasoline is passed by pump 12 at a pressure of about 60 p.s.i. and temperature of 110 F. through line 10 at a ow rate of about 125 barrels per hour into the bottom of a preliminary washing tower 14 through which is circulated 30-40 percent, typically 35 wt. percent, countercurrently, caustic soda solution in water in washing contact. The caustic is withdrawn from the bottom of tank 14 by way of line 16 controlled by valve 1S, the ow being forced by pump 20 through line 22 to the upper part of the wash tower 14 and distributed evenly in a washing spray through the ascending naphtha. The caustic spray through the ascending body of naphtha is continuously recycled at `the rate of about barrels per hour. From time to .time spent caustic containing a naphtha and alkyl phenols are withdrawn from the washing column 14 through line 24 as controlled by valve 26 `and replaced by another fresh caustic solution. The spent caustic is the source of aryl thiol catalyst 4in this example. The prewashed lnaphtha passed overhead of the column 14 through line 28 and thence to the bottom of a catalytic scrubber 30. Just before entering the scrubber 31, the washed naphtha has added thereto a continuously metered quantity of l cubic foot of air per barrel as supplied by rotameter 32 which controls a pressure regulator 34 through which compressed `air is passed from any source by way of line 36 into the naphtha line 28, the air and naphtha at the stated pressure entering the bottom of the scrubber 30. The scrubber is charged with a 40% caustic soda solution in water containing a small quantity of spent caustic from line 24, suicient to form a 0.5 wt. percent aryl mercaptan and at least 0.02. wt. percent phenol content solution. That catalyst solution is circulated in the same manner, the aqueous catalyst solution being drawn from the bottom of the scrubber 30 through line 38 controlled by vlalve 40 and passed by pump 42 by Way of line 44, reentening at a point near the upper end of the scrubber 30. The recycled caustic is sprayed into and scrubs the ascending mixture of naphtha `and air at a ow rate of about 20 barrels of catalyst solution per hour. The `aryl thiol catalyst is passed into the scrubber 30 by way of lines 46 and pump 4S, line 38 and pump 42 to supply and maintain the quantity stated of about 0.5% of aryl mercaptan in the caustic scrubber solution. The naphtha air catalyst scrubbing contact time is regulated to about 45 minutes. The scrubbed and catalytically treated naphtha is then passed overhead by way of line 50 into the bottom of a third scrubber 52 in which a simple 25 percent aqueous caustic solution is similarly circulated, the caustic being withdrawn from the bottom yof the tank through line 54, controlled by valve 56, and circulated by pump 58 through line 60 back to the top of the tank for scrubbing the sweetened naphtha with the relatively dilute caustic solution. The solution passed overhead of the third scrubber 52 by way of Aline 62 passes to a settling tank 64 from which the aqueous caustic is lallowed to settle and the supernatant clear sweetened naphtha is taken from the ltop of the settling tank by way of line 66 to the bottom of a water washing column 68 in which clear water introduced at la point near the top, through line 70, is passed in washing contact down through the naphtha to remove the last traces of entrained caustic, the water being ywithdrawn at the bottom through line 72, controlled by valve 74, and the washed sweetened naphtha is passed overhead .through line 76 to storage. The gasoline may finally be treated lwith any typical gum inhibitor for further stabilizing; for instance, it is treated with 0.002 wt. percent of ditertiary butyl paracresol.

EXAMPLE 3 A thermal cracked 125-430 F. F.B.P. gasoline containing 0.024 wt. percent RSI-I as sulphur is sweetened by a procedure illustrated in the flow diagram of FIG. 2. Sour naphtha is passed through line 80 by Wray of pump 82 into the lower end of caustic prewash tank 84 in which it ascends vertically against a 35 wt. percent aqueous caustic soda solution sprayed into a point near the top of the tank 84 from line 86, the caustic after descending through Iand washing the ascending column of naphtha being withdrawn from the bottom of tank 84 through line 88, controlled by valve 90, and recycled by pumps 92 for continuous washing of hydrocarbon. The gasoline is passed at 50 b-arrels per hour, at pressure of 100 p.s.i. and temperature of 175 F. From time to time spent caustic is withdrawn by way of line 92 controlled by valve 94 and replaced with similar fresh Istrong aqueous caustic. The spent caustic withdrawn can be used as a source of aryl mercaptan and also of petroleum phenols in the further treatment of this or another sour naphtha as described below. The caustic washed thermal gasoline passes overhead of the tank S4 through line 96 Iand enters a scrubber 98 at a point near the bottom. Just prior to entering the scrubber the gasoline is treated with 0.75 cu. ft. per barrel of air passed into the gasoline in quantity ybeing controlled by rotameter 100 passing thereto pressure regulator 102 mounted on a source of compressed air 104, `entering through line .106. The scrubber 98 has a catalyst scrubber solution circulated therein consisting of 40 wt. percent aqueous solution of sodium hydroxide tto which was added spent caustic withdrawn from line 92, sufficient to impart a 0.5 wt. percent of aryl mery'captan contained in the spent caustic, that aryl mercaptan consist-ing essentially of thiophenol, thiocresol v'and trace quantities of higher alkyl thiophenols. The spent caustic usually contains at least 5 wt. percent of phenols and alkyl phenols, suiiicient to impart a phenolic oil content to the catalyst scrubber solution of at least 0.2% and which gradually increases with subsequent additions thereto of spent caustic solution added to replenish the `aryl meroaptan content. The catalyst is circulated by withdrawing accumulated liquid catalyst solution from the bottom yof tank 98 through line 108, controlled by valve 110, by pumps 112 and passing the catalyst solution into the top of the scrubber tank 98 by way of line 114. The catalyst is circulated at the rate of about l5 barrels per hour against a naphtha flow rate of 50 barrels per hour from line 96, the naphtha leaving overhead by way of line 116 after catalyst contact with the air for a period of about 50y minutes. From time to time some catalyst solution is withdrawn and through lines 11S and 120 spent catalyst added, the flow being forced by pumps 122. From time to time spent caustic is added to the catalyst solution .to maintain the aryl thiol content in the range of 0.05 to 10 wt. percent Vin the scrubber solution, usually about 0.5 wt. percent and the phenol content becomes continuously increased 7 as more spent caustic is added and may be allowed to accumulate up to about 30 wt. percent of the scrubber solution. The caustic will be maintained in the range of about 2'5-40 wt. percent. The pretreated partially sweetened naphtha in line 116 has added thereto additional sweetening agent, ethylene oxide through line 124, the dow being forced by pump 126. The ethylene oxide solution may be handled as a dilute, about 10%, solution in a sweetened naphtha, preferably of the same character as the stock being sweetened and may be added in total quantity in the range of 5-100 lbs. per 1,000 barrels of gasoline, passing through line 116 usually 20-50 lbs. per 1,000 barrels and for purposes of this example 50 lbs. per 1,000 barrels lwas used. The partially sweetened thermal gasoline and ethylene oxide enters the lower end of fthe scrubber tower 12S through which somewhat more dilute aqueous, 1525%, caustic is circulated as a scrubber solution. The scrubber solution preferably contains 0.2-30% phenols, more usually 2-15 Wt. percent but no aryl mercaptan, and may be obtained as spent catalyst ,scrubber solution from the preceding scrubber 98. The scrubber 128 has its aqueous caustic solution withdrawn at the bottom through line 130, controlled by valve 132, the ilow being forced by pump 134 for recycle through line 136 from which it enters at a point near the top of the scrubber. The sweetened gasoline leaves'the sombber 128 overhead, passing by way of line 138 into a settling tank 140 Where, over a settling period of about 1 hour, most yof the caustic .is settled out. The settled aquevous caustic scrubbing solution withdrawn from the bottom of tank 140 rinto a line 142, controlled by a valve 134, and the supernatant sweet thermal gasoline is withdrawn through line 146. It is desirable sometimes for ultimate Sweetening, particularly 'when certain sweetening agents such the arylene diamines are used, to store the sweetened naphtha over caustic, usually at a raised temperature from ambient up to about 150 F. The sweetened naphtha in line 146, accordingly, is again mixed in line 154 with 15-25 typically 20%, caustic sod-a solu- .tion circulated by pump 150 drawing settled caustic from the bottom of storage tank 152 and passing the same through line 148 to join the .sweetened gasoline from .line 146. The caustic and sweetened gasoline have their temperatures adjusted to about 125 F. in the pipe mixer land heat exchanger 155. The warm mixture then passes into the settling tank 152 after being thoroughly inter- .rningled in their passage thereto. The sweetened naphtha in tank 152 can be stored over the caustic bottoms for any substantial time, sometimes 12 to 36 hours, but when nethylene oxide sweetening is used it may remain in storage tank 152 only :as little as 10 or 15 minutes to an hour, long enough to allow the caustic to settle from the naphtha. The sweetened naphtha is withdrawn from storage tank 152 through line 156 and passed to the bottom of a water washing tank 158 into which Water is introduced at lthe top through line 160 passing down ,countercurrently to the :ascending column of sweetened gasoline washing the same to remove last traces of caustic. The Water is withdrawn through line 162, controlled by valve 164 at the bottom, and the washed sweetened naphtha is withdrawn overhead through line 166 and sent to storage. If desired, the storage tank 152 may be by-passed through line 157 and sweetened naphtha in line 146 passed directly to line 156 and washed with water before storage. The excess oxygen contained in the injected air of each which has not been used up in oxidation and the residual nitrogen associated therewith Ican be removed from the system through a vent 159 controlled by a valve 161 responsive to the pressure in the system sensed through line 163 for removal of the gas from the settling tank 153.

Certain sweetening agents sensitive to oxidation such as ethylene oxide are more eiiiciently used after excess air is removed. For this purpose an air disengaging Air tank 115 may be mounted between scrubbers 98 and 123. That tank may be by-passed as described by way of line 116. However, where it is desirable to remove the air, the naphtha is passed through a line 117 controlled by `a valve 119 in the bottom of tank 115, in effect an air separating tank in which ran upper air layer accumulates above a lower naphtha layer. The naphtha is withdrawn and passed into line 116 -by way of a line 123 controlled by valve 121, and the air accumulating above the naphtha in tank 115 is bled off through a vent 125 controlled by pressure reducing valve 127, sensitive to the pressure 'in tank 115 yby way of line y129.` In this manner air is removed from the naphtha passing into thescrubber 128 before air-sensitive sweetening agent such as ethylene oxide is passed into the naphtha for the further sweetening thereof.

The following Table 2 compares the results available using aryl mercaptan catalyzed air sweetening applied both to light catalytic gasoline and thermal gasoline according to Examples 2 and 3, respectively, and using straight ethylene oxide treatment in the presence of l0 percent petroleum phenol and 25% aqueous caustic solution according to my prior Patent 2,862,804 as a comparative standard.

Table 2 Light Cat. Gasoline Thermal Gasoline Air Catalyst Ethylene Oxide Ethylene Ethylene Oxide Air Catalyst Oxide Gasoline Quality:

BSH, Wt. percent:

Raw Treated Induction- Raw (Inhibitor Added) Treated Color-(Saybolt) Raw Treated Further comparison is made of costs of treatment of Example 2 compared to the treatment of Example 3.

Table 3 Light Cat. Gasoline Thermal Gasoline Treating Costs Ethylene Ethylene Oxide Air Oxide Ethylene Oxide:

Lbs/1,000 Bbls.-. Cents/Bbl.

Caustic, Lbs/1,000 Bbls Inhibitor:

Lbs/1,000 Bbls Cents/Bbl cubre ist/Bbl.

Cents/B bl Total Cost, Cents/Bbl meno 000 lo cn It will be noted that in the treatment of light catalytic gasoline the mercaptan catalyzed treatment produces a product of lower RSH content, so that as a sweetenng method it is superior -both as to cost and sweetening effect. However, it slightly reduces the stability of the gasoline so that greater quantities of inhibitor as well as caustic are used. A surprising eifect, however, is that despite use of such greater quantities of stabilizer, there is a comparative reduction in total costs. In the instance of thermal gasoline mercaptan catalyzed air sweetening, followed by ethylene oxide, sweetener is applied. It willV be noted, however, that there is substantial reduction in the quantity of ethylene oxide that would be used with same ultimate caustic cost. Even though some larger quantity of inhibitor is necessary, there is still a large net saving over the known ethylene oxide. The same `favorable comparison results when other sweetening agents such as the phenylene diamines or polyhydric phenols, as listed above, are used for the `secondary sweetening treatment.

EXAMPLE 4 A coker distillate B.P. 160-425 F. having 0.035 wt. percent RSH as sulphur is treated following the procedure of Example 3 as to preliminary caustic wash and initial air sweetening, using 1 cu. ft. of air per barrel, the naphtha being treated at 150 F. and at fa pressure of 100 p.s.i., and catalyzed with phenolic caustic containing about 0.5 wt. percent of aryl mercaptan and 10 wt. percent of phenols, the phenol and mercaptan being derived by additions of spent preliminary wash caustic to a commercial 40 wt. percent caustic soda solution in water. The flow rate of the naphtha is at about 45 barrels per hour against a catalyst flow of 17 barrels per hour. Thereafter, the partially sweetened naphtha had 7 pounds per thousand barrels of N,Ndi isobutyl p-phenylene diamine added thereto as it passed into a second scrubber operating under the same flow conditions. That scrubber solution was a 25 wt. percent caustic soda solution in water, also containing wt. percent of phenols :obtained from spent caustic. The finally sweetened naphtha contained 0.0003 wt. percent RSH -as sulphur.

EXAMPLE 5 In a modified procedure, Example 2 was repeated but with the variation that the catalyst solution was modified to contain catechol in quantity of 0.5 percent. The light catalytic gasoline of the example, again Itreated with the modified catalyst solution, had its RSH content reduced t0 0.0002 wt. percent yas sulphur, but it was found to have an induction period of 600, thereby indicating that a sweetening agent such as a polyhydric phenol which inherently has high `antioxidant effect when added to the aryl mercaptan catalyst solution in caustic, both improves the sweetening and inhibits oxidation of the hydrocarbon per se, imparting a higher induction period. A comparable improvement .is available in d-iiiicultly sweetened sour naphthas such `as thermally cracked or coker distillates. However, the net effect is not as good upon such .difcult to sweeten naphthas as when a separate sweetening treatment is applied in a subsequent scrubbing stage as shown in FIG. 2 and described in Examples 3 and 4, using an additional scrubbing step with the sweetening agent of the character of an epoxide `or a phenylene diamine.

As thus described, an improved air sweetening method is made available by treatment of sour liquid hydrocarbon by catalyzing the air sweetening with catalyst comprising aryl mercaptan in strong aqueous caustic solution. That catalyst solution preferably further contains at least 0.02 to 30 percent of phenols, usually 2 to 15 percent. This catalyzed air sweetening is effective to sweeten the usually diflicult to sweeten caustic insoluble sour components. For that reason it is most economic to rst treat the liquid hydrocarbon in a preliminary wash with strong aqueous caustic to remove caustic soluble components comprising essentially the aryl mercaptan and naturally `occurring petroleum phenols. The caustic prewash of sour distillate, accordingly, produces a spent caustic which `also becomes an economic source for subsequent supply to the caustic catalyst Ifor air treatment in quantity -suliicient to impart the desired aryl mercaptan as welll as phenol content thereto. Thus the preliminary caustic washing step produces the desired phenol and aryl mercaptan solution in the spent caustic, useful in the catalysis of the air sweetening, as well as a par- 10 tially sweetened naphtha, containing/only the caustic insoluble sour components for which the `air sweetening rby this catalysis is effective. This treatment `alone sufices as adequate sweetening for many easily sweetened naphthas such as light catalytic gasoline, and for some distillates which do not need extensive sweetening. However, Kfor more extensive sweetening, some sour liquid hydrocarbon, difficult to sweeten, such las thermal or coker gasoline may then have .applied an additional sweetening of a known type. Such additional sweetening may comprise adding to the naphtha or to the catalyst solution itself 0.05 to 1%, usually 0.1 to 0.5 wt. percent of a polyhydric or amino phenol, which imparts further oxidation stability as well as improved sweetening to the aryl mercaptan catalyzed air sweetening treatment.

Alternatively, such Asweetening as organic epoxide typically ethylene oxide or propylene oxide is applied to the preliminarily air sweetened liquid hydrocarbon, usually by caustic scrubbing the hydrocarbon lafter dissolving a small quantity of the organic epoxide, the -caustic scrubbing being -with ya relatively dilute caustic such as 15 to 25 percent aqueous-caustic and .to which preferably is added `0.02 to 30 percent of phenols which catalyze the epoxide reaction, as taught in my prior patent, with the advantage, however, that the use herein of organic epoxide yapplied with a preliminary air `sweetening step upon the hydrocarbon is a substantial economy.

Other sweetening agents such as the phenylene diamines typically N,N di-lower alkyl phenylene diamines may `also be used for further treatment of the air sweetened liquid hydrocarbon, the arylene diamine treated partially presweetened naphtha being further scrubbed with aqueous caustic such as a 15 to 25 percent aqueous caustic, `desirably but not essentially also containing some phenol, such as 0.02 to 30 percent phenol. Similar to known arylene diamine `sweetening procedures, the diamine scrubbed sweetened naphtha may optionally then be bot-h epoxide and arylene diamine stored `over aqueous caustic `such as a 15-25% solution.

The total sweetening procedure hereof may be applied at ambient temperatures, lbut preferably are applied at slightly raised temperatures and -at higher pressures, at least for better 'air contact, such yas from 50100 psi. and at temperatures up to about 212 F.

It is usually preferred for ordinary gasolines to use a temperature in the range of 70-150 F. and for heavier liquids and liquids containing greater quantities and more difhcult to sweeten sour components, such as thermally cracked, color distillates and fuel oil to use -212" F. The air is used in quantity of about 1A to 2 cu. ft. per barrel. It is usually ordinary air but it may be enriched or replaced with equivalent oxidizing agents. For ow rates the gasoline may be passed at any desired rate, typically 25-125 barrels per hour against a circulation rate of catalyst of about 5-50 barrels per hour, the higher rates such as above barrels per hour being more usually for the easily sweetened liquid hydrocarbon, and the lower rates for the more difficult to sweeten.

Various modifications will occur to those skilled in the art; for instance, the aryl mercaptan may be of various types and selected from pure synthetic rather than the natural petroleum solutions with some sacrifice of economy, as desired. The initial caustic wash may be omitted, again, with sacrifice of economy; and other epoxides, phenols, polyhydric phenols, amino phenols and diamines for these sweetening treatments may be applied following the preliminary catalytic step. Accordingly, it is intended that the description herein be regarded as illustrative and not limiting except as defined in claims appended hereto.

I claim:

1. The method of sweetening a sour hydrocarbon naphtha containing a small quantity of sour components not exceeding 0.1% mercaptan, calculated as sulfur, comprising first washing the said sour naphtha with strong aqueons caustic solution to remove substantially all alkali soluble components, and then sweetening the residual alkali insoluble components in said naphtha by Washing the same with a strong aqueous caustic solution containing from 0.1 to 10% of aromatic mercaptans and at least 2% of phenols in the presence of an oxygen-containing gas.

42. The method as defined in claim 1 wherein the naphtha is catalytically cracked naphtha. 3. The method of sweetening a sour hydrocarbon naphtha containing a substantial quantityof sour components up to about 0.1% mercaptan,V calculated as sulfur, comprising irst washing said sour naphtha with strong aqueous caustic solution to remove substantially all alkali soluble components, sweetening the residual alkali soluble components in said naphtha by Washing the same in the presence of oxygen-containing gas with a strong aqueous caustic solution containing 0.1 to 10% of aromatic mercaptans and at least 2% of phenols, separating the naphtha and introducing a small quantity of an organic epoxide, and nally Washing the naphtha solution with strong aqueous caustic containing at least 2% of phenols.

4. The method as defined in claim 3 wherein the naphtha is sour thermally cracked gasoline.

5. The method of sweetening a sour hydrocarbon naphtha containing a substantial quantity of sour components up to about 0.1% mercaptan, calculated as sulfur, comprising first Washing said sour naphtha with strong aqueous caustic solution to remove substantially all alkali soluble components, sweetening the residual alkali soluble components in said naphtha by washing the same in the presence of oxygen-containing gas with a strong aqueous caustic solution containing 0.1 to 10% of aromatic mercaptans and at least 2% of phenols, separating the naphtha and introducing a small quantity of an'N,N'-dilower alkyl p-phenylene diamine, and nally Washing the naphtha solution With strong aqueous caustic containing at least 2% of phenols.

6. The method as delined in claim 5 wherein the naphtha is sour thermally cracked gasoline.

References Cited in the file of this patent UNITED STATES PATENTS 2,552,399 Browder May 8, 1951 2,862,804 Petty Dec. 2, 1958 2,916,442 Niehaus et al Dec. 8, 1959 

1. THE METHOD OF SWEETENING A SOUR HYDROCARBON NAPHTHA CONTAINING A SMALL QUANTITY OF SOUR COMPONENTS NOT EXCEEDING 0.1% MERCAPTAN, CALCULATED AS SULFUR COMPRISING FIRST WASHING THE SAID SOUR NAPHTA WITH STRONG AQUEOUS CAUSTIC SOLUTION TO REMOVE SUBSTANTIALLY ALL ALKALI SOLUBLE COMPONENTS, AND THEN SWEETENING THE RESIDUAL ALKALI INSOLUBLE COMPONENTS IN SAID NAPHTHA BY WASHING THE SAME WITH A STRONG AQUEOUS CAUSTIC SOLUTION CONTAINING FROM 0.1 TO 10% OF AROMATIC MERCAPTANS AND AT LEAST 2% OF PHENOLS IN THE PRESENCE OF AN OXYGEN-CONTAINING GAS. 